Process Indicators And How They Work

Process Indicators

Since 1880, when the first steam sterilizer was created by Charles Chamberland, biomedical professionals have been working on methods to monitor and validate the sterilization process. Biological and chemical indicators were introduced and routinely used around the late 1940’s and early 1950’s, but still it was believed these were not always accurate.

Sterility assurance monitoring for sterilization has since become much more complex in today’s healthcare environment and most consist of: 

  • Physical monitoring
  • Chemical sterilization indicators
  • Biological indicators
  • Sterilizer maintenance
  • Accurate record keeping

The Association for the Advancement of Medical Instrumentation (AAMI) and the International Organization for Standardization (ISO) have defined chemical indicators as a sterilization monitoring device designed to test the parameters for sterilization have been met. Through a comprehensive quality control program, chemical indicators will show malfunctioning equipment and technical errors that could result in not sterilizing devices properly. Utilizing chemical indicators during the sterilization process ensures confidence in the reprocessing of medical devices. 

How do Chemical Indicators work?

Chemical indicators monitor sterilization processing with the use of sensitive chemicals that change color when exposed to high temperatures or combinations of time and temperature per CDC website. Results are visible immediately following the sterilization cycle to verify that the sterilization cycle has been completed successfully. Examples of chemical indicators include tapes, strips, tabs and special markings on packaging material. The physical or chemical change in the sensitive chemicals can be visibly seen and will result in the pass or fail of sterilization.

Chemical Indicator Types

Chemical sterilization indicators have been divided into six types with specific performance requirements per AAMI ST-79.

Types of Chemical Indicators What they indicate Application Example
Type 1: Process Indicators
  • Exposure to the sterilization process
  • Help differentiate between processed and unprocessed loads
Indicator tape or indicator labels that are placed on the outside of a pack
Type 2: Specific Use For use in specific tests as defined by standards Bowie Dick test used to check the efficiency of the air removal and steam penetration within the chamber
Type 3: Single Variable React to one critical parameter A chemical pellet which melts at a specific temperature Rarely used in healthcare
Type 4: Multi-Variable React to two or more critical parameters Measure’s temperature held for a specific amount of time Rarely used in healthcare
Type 5: Integrating Indicators React to all critical parameters over a range of sterilization cycles Moving front indicators placed inside packs and can be used on a variety of sterilization cycles Most common chemical indicator for Pack Monitoring
Type 6: Emulators, or cycle specific indicators React to all critical parameters for specified sterilization cycles Strips placed in packs that respond to and monitor specific cycles (i.e. Prevacuum 270°F/132°C, 10-minute steam sterilization cycles) Example: Extended Cycle Monitoring


Table provided by Steris

How to use Chemical Indicators

The type of indicator used and how it is placed will be determined by your sterilizer, the sterilization process you are testing and the items being sterilized. 

External indicators are used on individual items to indicate whether a medical device has been processed or unprocessed. This is the most basic of the indicators and generally a Type 1 or Type 2 indicator is all that is needed. 

Internal indicators are used inside each package that is being sterilized. Generally, Type 3, 4, 5 & 6 chemical indicators can be used in these circumstances to show that the package and contents of the package have been processed or sterilized. Type 5 & 6 are often the preferred chemical indicator as they offer the most information on critical sterilization parameters. 

ERD is your sterilizer maintenance service provider

If you are concerned that your sterilizer is working incorrectly, or your chemical indicators are showing inconsistencies, call ERD and our biomedical technicians will perform the necessary maintenance to meet your quality assurance needs. 

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